2020-2021
  • Electron microscopy (EM) is an electron 
   beam  which  is  focused  into  a  small 
   probe across the surface of a specimen. 
   The  first  electromagnetic  lens  was 
   developed  in  1926  by  Hans  Busch. 
   Electron  microscope  follows  the  same 
   principle of compound microscope, but 
   uses electrons beam as an illumination 
   source instead of light. 
   Electron microscopes allow biologists to 
      explore cells in more details 
  • To observe the organelles such as: 
   Mitochondria, Ribosomes, Endoplasmic 
   reticulum (ER), Golgi apparatus and 
   Lysosomes.
  • Heavy metals (such as lead) are used to 
   stain cells prior to examine via EM. The 
   stain is more visible in organelles than in 
   the surrounding cytoplasm. Defects in a 
   cell’s organelles are easily seen
      Electron microscopes are used in the scientific laboratories and many industries, such as forensics, nanotechnology and mining.
                                        
     • Disadvantages of electron microscopes
     • 1- It is a large machines 
     • 2- Training is required
     • 3- It is very expensive
     • 4- Specimens are required a lot of 
        preparation. 
     • 5- The specimens are mounted in plastic, 
        which means that only dead cells can be 
        viewed. 
    There are two types of electron microscopes
  • Scanning electron microscope (SEM) 
  •  The mode of action for the SEM is similar to 
    compound microscope however, an electron 
    beams behave like waves which focus via 
    using a magnetic field rather than uses of 
    ordinary lenses. Metallic coating is required 
    for  the  biological  specimens.  The  electron 
    microscopes  are  used  to  achieve  up  to 
    100,000x magnification and more than 1000 
    x resolution than the light microscope. 
         Components of the SEM
  • 1- Lens: It is an electrical field and are not 
   the optical materials (like glass
  • Electron optics: 
  • a- Condenser lens: It is focusing the electron 
   beam to the objective lens. 
  • b- Objective lens:  It is responsible for size of 
   electron beam impinging on sample surface
  • 2- Electron beam.
  • 3- Transducers (detectors).